1. Field of the Invention
The present invention relates to a cement composition containing dextrin, and more particularly to a cement composition containing dextrin which suppresses the temperature rise of concrete and mortar due to the heat of hydration.
2. Prior Art
In recent years, civil engineering and building constructions are enlarged in scale with attendant increase in mass concrete works. Generation and accumulation of heat due to hydration of cement is increased with the increase in size of the constructed mass so that the temperature of the cement mortar or concrete is abruptly raised particularly at the initial stage of ageing to cause internal stresses after cooling to thereby create a so-called thermal cracking problem in the finished mortar or concrete. Such thermal cracking problem is caused when a normal cement is used, and the tendency to create this thermal cracking problem is further promoted when there is used an expansive cement which has been conventionally employed for compensating dry shrinkage or for realizing a special effect in the chemical pre-stressing process, since the hydration reaction of the expansive cement is accelerated as compared to that of the normal cement.
Anyway, this thermal cracking problem may be prevented, for example, by the following measures:
(1) The amount of a cement mixed in the unit volume of the concrete or mortar is decreased.
(2) A cement which generates a smaller quantity of heat of hydration is selected.
(3) Pre-cooling or pipe cooling is effected.
(4) The quantity of concrete or mortar charged at every unit operation is lessened.
(5) Shrinkage joints are provided.
(6) Ageing is strictly controlled.
However, difficulties are encountered to effectuate the aforementioned measures in the practical construction works due to various limitations. Under these circumstances, it is a conventional practice to add a small amount of an additive such as an additive mainly composed of a lignin sulfonate, an additive mainly composed of an oxycarboxylate or sugar. However, it as been difficult to suppress the temperature rise in the molded bodies at the early ageing stage and to prevent the thermal cracking by means of the prior art additives mentioned above, since an abrupt hydration reaction takes place after a certain delay in commencement of the hydration reaction, neverthless they are effectively used for retarding the commencement of the hydration reaction.
In the meanwhile, the concept of adding dextrin to cements has been known in itself, for example from the disclosure of U.S. Pat. No. 3,414,420. This U.S. Patent discloses a retarded oil well cement used for a special application, which comprises an oil well Portland cement admixed with a retarder consisting of 1 to 8 parts by weight of a modified starch to 1 part by weight of dextrin. Namely, dextrin is used together with a special starch to retard the setting of the cement. However, this U.S. Patent neither discloses nor suggests the cement composition of the present invention containing a specified amount of dextrin having a cold-water solubility within the range as described hereinafter and defined in the appended claims so as to suppress the temperature raise at the early ageing stage thereby to prevent the thermal cracking.
U.S. Pat. No. 3,486,960 discloses a method of coating a substrate with tile wherein the tile is adhered to the substrate in spaced edge to edge relationship, the improvement comprising filling the spaces between the tiles with an adhesive grout prepared by mixing with water a dry composition comprising hydraulic cement and non-ionic dextrin. This method is directed to a method of setting tiles using a cement composition containing non-toxic dextrin for providing water-retentivity, and also fails to disclose or suggest the cement composition of the present invention containing a specified amount of dextrin having a cold-water solubility within the range as as set forth above similarly as the U.S. Patent referred to formerly.